The present disclosure relates to a piezoresistive micromechanical sensor component and to a corresponding measuring method.
Although applicable to any piezoresistive micromechanical sensor components, the present disclosure and the problem which it is intended to resolve will be explained with reference to a piezoresistive micromechanical acceleration sensor.
Modern acceleration sensors are conventionally evaluated capacitively. The piezoresistive evaluation which is also practiced, however, offers greater potential with regard to the desired ever increasing miniaturization. In the case of piezoresistively evaluated acceleration sensors, here referred to as piezoresistive acceleration sensors, distinction may essentially be made between the following two variants.
One variant consists in structured doping, piezoresistors being doped at the positions on a bending beam where the maximum mechanical stress occurs during deflection.
The other variant consists in homogeneous doping, the entire homogeneously doped bending beam being used for the evaluation. To this end, a homogeneously distributed mechanical stress is required in the beam. Since the entire bending beam is used for the evaluation in the case of homogeneous doping, homogeneous doping offers advantages with regard to miniaturization.
J. Micromech. Microeng. 15 (2005), pages 993-1000 (Shusen Huang et al.) discloses a piezoresistive micromechanical acceleration sensor comprising homogeneously doped bending beams.
FIG. 6 is a perspective view of this known piezoresistive micromechanical acceleration sensor.
In FIG. 6, reference 1 denotes a substrate on which a sacrificial oxide layer S1 and a cover layer S2 are provided. Structured out of the cover layer S2, there is a seismic mass 3 which is anchored via an undoped bending beam B to the substrate 1. At the tip of the seismic mass 3, a stop 30 is provided, which protects the seismic mass 3 against excessive deflections. Below the seismic mass 3 and the bending beam B, there is a cavity K.
Next to the bending beam B, the seismic mass 3 is connected via two homogeneously doped piezoresistive beams PR1, PR2 to the substrate. In order to record a resistance change of the piezoresistive beams PR1, PR2 when the seismic mass 3 is deflected in the substrate plane, metallization regions M1, M2, M3, M4, M5 are provided, which are interconnected with the piezoresistive beam PR1, PR2 so as to permit half-bridge evaluation.
For signal feedback from the seismic mass 3 to the substrate 1, in this circuit arrangement the bending beam B is fundamentally necessary in addition to the piezoresistive beams PR1, PR2. The additional bending beam B, however, reduces the mechanical sensitivity and/or increases the process outlay with respect to the required trenches, when otherwise assuming the same requirements. In particular, trench isolation (STI) which is as narrow as possible is required between the beams PR1, B, PR2, which entails increased process outlay.